The present invention relates to a pattern inspection method and apparatus for producing an image of an object such as a semiconductor wafer, a TFT or a photomask using an electron beam or light and comparing the image-with a reference image stored in advance thereby to detect a defect, or in particular to a pattern inspection method and apparatus suitable for inspecting a semiconductor logic product using the electron beam.
The prior art disclosed in JP-A-5-6928 (prior art 1) and JP-A-10-74812 (prior art 2) for pattern inspection to detect a defect by comparing continuously input canditate (object) images with a reference image are well known.
The prior art 1 concerns a pattern inspection method and apparatus in which the shift amount (displacement amount) between a detection binarized edge signal indicating a detection edge pattern from a detection image signal detected by a linear image sensor and a reference binarized edge signal indicating a reference edge pattern from the reference image signal obtained by delaying the repeated chip pitch is detected by a non-coincidence detection circuit for each area scanned two-dimensionally by the linear image sensor and stored in a status storage unit. In the case where the present detection result stored in the status storage unit is different from the result of detection by the non-coincidence detection circuit in the preceding inspection, a positioning circuit is controlled in accordance with the preceding shift amount or a predetermined shift amount as well as the present shift amount, so that a common non-coincident pixel indicated by the comparison of the binarized edge signal with each shift amount in a defect determining circuit is determined as a defect. The prior art 1 also includes the description that a detection error for determining the normal portion as a defect due to the positioning condition is reduced. In other words, according to the prior art 1, the range in which a displacement occurs is enlarged and only a common non-coincident pixel, if any, is determined as a defect.
The prior art 2, on the other hand, concerns a method in which an image signal of a repetitive object pattern is continuously detected and the object pattern is inspected based on the image signal thus continuously detected. The prior art 2 thus includes the description that the image continuity is determined using the displacement amount information of the past images as well the current image in the process of positioning a plurality of images, and the inspection sensitivity of the boundary portion of discontinuous images is controlled based on the image continuity.
Both the prior art 1 and the prior art 2, however, lack the consideration of any means to reduce the chance of erroneously detecting a normal fine pattern coexisting with various fine patterns within a die (chip) of an object and to prevent the overlooking fine detects included in the fine patterns.